Process of defecating cane juice



Patented Nov. 15, 1932 UNITED STATES PATENT 'OFFIQE TRUMAN B. WAYNE, OF HOUSTON, TEXAS, ASSIGNOR TO NATIONAL ALUHINA'EE COB- PORA'IION, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE PROCESS OF DEFECA'IING CANE JUICE Ho Drawing.

its availability as crystallizable sucrose in the pan-boiling operations which follow.

The process is especially applicable to the purification of raw cane juices such as are expressed from sugar cane in raw sugar factories, and with certain obvious modifications may be em loyed on other syrups found in raw sugar actories and refineries.

Cane juice expressed from the mills is customaril clarified or defecated with lime. The ob ect of this clarification is to remove from the juice the maximum quantity of impurities at the earliest possible stage of the process. Different juices from different localities, or even from the same locality, differ greatly in the amount of lime necessary for proper defecation, but in general suflicient lime is added to neutralize the organic acids present and produce a complex, flocculent precipitate of organic and inorganic constituents of the juice which mechanically envelop and carry down finely divided suspended matter.

It is now well known that the degree of clarification has a great bearing on the efiiciency of operations at subsequent stations in the factory-the pan-boiling, the centrifugalizing of the sugars, (especially the low goods) the quality of the products, and of most im-' portance-the yield of raw sugar. In addition, efiicient clarification reduces time-losses and expense due to cleaning fouled apparatus. This is of prime importance in factory operation and fuel economy. .7

When the raw sugars go to the refinery to be made into refined sugars, deficiencies in clarification at the raw sugar factory again Application filed September 8, 1930. Serial No; 480,609.

come to the front and result in slowing down the filtration and other purification processes of the refinery; as well otherwise manifesting themselves in reduced yields, increased costs,

and by their adverse effect on the quality of the finished product.

Much evidence has been accumulated that the phosphate content of the raw juice is the major factor in efficient clarification. Many investigators have independently established this fact, and it has also been shown that it was immaterial whether the phosphate was naturally present or added subsequently. The elimination of colloids was found to be a direct function of the percentage of phos phorous pentoxide (P 0 present when lime is used to raise the alkalinity of the juice to a given hydrogen-ion concentration (pH). About twenty per cent of the precipitate is ash which has been shown to consist principally of calcium oxide (CaO) and phosphorous pentoxide (P 0 with appreciable quantities of magnesium, aluminum and iron.

Defecation, therefore, is essentially an inorganic reaction in which the flocculent precipitate of calcium phosphate and other insoluble salts mechanically carries down with it the coarse suspended matter and adsorbs some of the colloids. Hardly more than five per cent of the total non-sugars, other than that originally present in suspension, in the juice are removed by the usual lime defecation process. For these reasons, other inorgamc chemicals such as sulfurv dioxide or phosphates have been used to some extent with lime to aid in the removal of the impurities.

The usual defecation process with lime removes only a small proportion of the impurities in the juice, probably because the proportion of inorganic constituents of the juice capable of reaction with lime to produce the desired flocculent precipitate is too small to carry down a consldera 1e proportion of the organic non-sugars. The use of morganic acids and salts in connection with lime mcreases the non-sugar elimination because of the greater volume of inorganic precipitate produced. However, many of these defecatmg agents cause practical difliculties in factory operation, such as scaling of evaporators, difliculty at the mud press station,

etc.

My present invention, however, on the other hand, avoids the above-mentioned difliculties and produces clearer, brighter, and purer clarified juices. There is a marked reduction in the objectionable iron-polyphenol compounds which discolor clarified cane juices after standing, and also a considerable elimination of such encrusting inorganic constituents as silica, iron, and magnesia from the juices treated by my process.

I accomplish this result by the addition of a solution of a soluble aluminate, preferably sodium aluminate, to the raw juice followed by the addition of lime to produce an inorganic precipitate of calcium aluminate and possibly some aluminum hydroxide ,which entangle and adsorb some of the organic non-sugars, and thereby produce a better clarification: The sodium aluminate, in

the proportion of from 0.25 to 1.0 lb. of dry sodium aluminate (or its equivalent of the commercial liquid sodium aluminate) per 1000 gallons of juice is preferably added to the cold or heated raw juice and thoroughly mixed in to allow any reactions between it and the inorganic constituents to occur that will, and this is followed by the addition of lime sufficient to raise the alkalinity of the juice to pH 8.3-9.0 after which the chemically treated juice is heated to 210220 F. to produce the desired coagulation (break). The amounts of sodium aluminate and lime which must be used depend on the characteristics of the raw juice, and this can be readily determined by those skilled in the art of clarifying cane juice.

The sodium aluminate and lime may be mixed prior to adding them to the juice, but it has been found that the results are not as satisfactory as when they are added sepa-- .marked coagulating and precipitating effect when the juice is heated.

It is probable, also, that some of these inorganic constituents are intimately associated with the organic non-sugars, and when precipitation occurs within the solution more of the latter are adsorbed and entangled by the inorganic precipitates than would be the a case if the sodium aluminate was allowed to In this connection I wish to point out that it has been proposed to treat strongly limed raw beet-juice with sodium aluminate for the purpose of removing therefrom the excess of lime. For example, in United States Patent No. 1,578,463, granted to Nicholson and Beal, there is described and claimed a process of treating limed ,beet-juice with sodium aluminate. The primary object of these in ventors was to remove the excess of caustic lime left in the juice when treating it with caustic lime after comin from the diffusion battery of a beet mill. In the manufacture of beet sugar an alkaline juice is encountered all through the factory because the composition of beet juice is such that high alkalinities may be carried. In cane juice defecation, however, high alkalinities cannot be carried owing to the presence of reducing sugars which are decomposed by an excess of lime to form dark colored decomposition products which will later interfere with the extraction of sugar from the juice as well as adversely affect the quality of the sugar produced. For that reason, although the first step in a beet factory is to lime the juices to a high alkalinity, in a cane factory this cannot be done.

In a-beet factory the lime is put in first and then removed with other agents, such as carbon dioxide, etc., and-Nicholson and Beal proposed to use sodium aluminate for the re-' moval of this lime instead of the usual agents such as carbon dioxide, etc. They neces- 1sarily then must add the sodium aluminate ast.

In a cane factory, however, the juice is limed to a little above neutrality and the re action between the lime and the constituents of the juice produces the clarifying effect and no treatment follows to remove the excess of lime. In the first place an excess of lime could not be used owing to the destruction of the reducing sugars and for that reason there is no large excess to remove. Liming when properly done usually, leaves less lime salts in the juice than were present before the defecation process occurred.

Now in accordance with my present invention, I-propose to add sodium aluminate to the raw cane juice to augment artificially the bodies within the raw juice that will produce a flocculent precipitate with lime. In addition, the sodium aluminate neutralizes some of the organic acids of the raw juice and forms insoluble heavy metallic salts which are then flocculated by the change in the hydrogen-ion concentration caused by the addition of lime. Cane juice contains considerable proportions of natural phosphates and compounds of calcium, magnesium, and silicon which produce flocculent precipitates when heated with lime.

However, the proportion of these precipitate-forming materials is too low efiectua 1y to remove a very large proportion of the much larger ratio of the organic non-sugars present. For this reason if sodium aluminate is added to the raw to increase the proportion of floc-forming reactive bodies and also to have a desirable effect on the natural bodies of this character in the juice, it causes the precipitation of a most satisfactory precipitate with lime.

It was found in my experimental work that the use of sodium aluminate in the raw juice ahead of the lime produced an entirely different effect from that produced by liming first and adding sodium aluminate later. In the latter case the sodium aluminate reacts with the lime to form calcium aluminate and the clarifying action would be purely me-' chanical instead of the more thorough efi'ect produced by getting the aluminate intimate- 1y mixed with the natural floc-forming constituents of the juice and then precipitating the entire mass with lime.

As a specific example of one method of carrying out my invention I will now describe the defecation and settling of raw cane uice.

The raw cane juice expressed from the mills is pumped to a small mixing tank or receptacle where sodium aluminate solution of any convenient strength, preferably 20 Be, is added either continuously or intermittently in the proportion of from 0.25 to 1.0 lb. of dry Na2A12O4 per 1000 gallons of raw juice. Another convenient method is to mix the sodium aluminate solution with the juice by injecting it by means of a roportioning pump into the juice line leading to the liming tanks.

The raw juice containin the sodium aluminate solution is then lime either cold or hot, depending on the preferences of the operator, in any convenient apparatus and unless it has been heated reviously is pum through the juice eaters and heated to 210220 F. and sent to the settling tanks. Thedatter may speclal design such as the Dorr clarifier, etc. wherein the flocculent precipitate is settled out and the clear juice sent to the evaporators. The muds may then be sent to the filter presses or otherwise disposed of, depending on the process employed in each actory.

It is also contemplated that the method of juice clarification herein described can be applied to the so-called compound clarification method wherein the hi h and low ur ity juices are separately de ecated an the low purity defecated uices are then a in them to the high pun raw uices. Y

The clear efecat juice is then evaporated to a syrup in the usual evaporators and be of conventional type or or modifications in the various processes which may be used in the manufacture of raw or white sugar from juice defecated by my process, as it is intended that the step of defecating can juice with lime and a soluble aluminate be applied to any existing process, whether patented or not, to improve said processes, and that said improved defecation process, alone, is the subject of my claims.

The sodium aluminate reagent above described may be a solution containing various percentages of N a Al O in the presence of NaOH and/or mp0,, but the free alkali content should be as low as is permissible for a stable sodium aluminate solution. The presence of Na CO. is to be preferred over N aOH because of its smaller soda alkali content, and because the CO3 radical forms an insoluble precipitate of (30.00,; with the lime added in the defecation, process. The aluminate radical is precipitatedas insoluble calcium and magnesium aluminates, and probably partly as aluminum hydroxide.

It is to be understood that other water soluble or cane juice soluble aluminates may be employed or substituted for sodium aluminate with effective results, although sodium aluminate is preferred, because it is cheaper and more easily obtained. Thus, barium aluminate, in water soluble form, may be subped stituted for the sodium aluminate herein dis closed when following the teachings of the present invention.

Furthermore, I do not wish to be limited to the exact amounts of materials herein s ecified nor to the exact details as to proce ure, but claim as my invention:

1. Process of defecating cane juice which ion comprises treating the same with a soluble I aluminate followed by addition of lime.

2. Process of defecating cane juice which comprises treating the same with sodium aluminate followed by theaddition of lime.

3. The process of defecating cane juice which comprises treating the same with a solution of sodium aluminate followed by the oxide. 4. Tlle process of treatin addition of a suspension of calcium hy-. treated with clarifying agents after ad g dr raw sugar-cane juice which comprises addmg thereto from 0-25 to 1.0 lb. of sodium meta-aluminate per 1,000 gallons of juice, followed later by the addition of lime.

5. The process of treating raw sugar-cane juice which comprises adding thereto from 0.25 to 1.0 lb. of sodium meta-aluminate per 1,000 gallons of juice, followed later by the addition of calcium hydroxide, and then heating the resulting mixture to from 210220 F. thereu on allowing the impurities precipitated y this treatment to settle, and withdrawing the purified cane-juice.

In witness whereof, I have hereunto subscribed my name.

TRUMAN B. WAYNE. 

